This invention relates to the cogeneration of electricity and refrigeration during the reduction of pressure of pipeline gas. More particularly, the invention achieves such cogeneration with a simple, integrated system utilizing only a small amount of energy.
It is well known that pipeline gas usually at a pressure of at least 150 psia (pounds per square inch absolute) can be passed through an expansion engine to reduce its pressure and to convert the work abstracted from the gas into electricity with an electrical generator driven by the engine. The greater pressure reduction effected in the expander, the greater is the work performed (i.e., the greater is the generation of electricity) and also the greater is the temperature drop in the expanded gas which means the greater is the refrigeration produced. Hence, increasing the cogeneration of electricity and refrigeration depends on increasing the pressure drop of the expanded gas.
Two problems arise when designing a system to maximize the cogeneration of electricity and refrigeration by the work-expansion of pipeline gas. The first problem is that pipeline gas invariably contains moisture which must be removed before the gas is expanded to avoid icing and gas hydrates that impair the operation of the expander and possibly damage it. The other problem is that the cold, expanded gas cannot be discharged into a distribution system because temperatures of 32.degree. F. and lower can lead to troubles such as embrittlement of the pipeline, leakage at pipe joints and freezing of ground water leading to ground heaves and stressing of the pipeline.
Elimination of both problems is simple enough. The gas must be dehydrated before it is work-expanded and the cold, expanded gas must be warmed before it is introduced into the distribution system. Both solutions require the expenditure of energy and therefore have an important impact on the financial feasibility of a cogeneration project.
Accordingly, a principal object of this invention is to cogenerate electricity and refrigeration by the work-expansion of pressurized pipeline gas while integrating the dehydration of the pipeline gas with the heating of the cold, expanded gas to curtail the expenditure of energy.
Another important object is to provide a simple, integrated cogeneration system in which the energy required to effect both gas dehydration and heating of the expanded gas is supplied solely to the dehydration operation.
These and other objects and advantages of the invention will be evident from the description which follows.